This invention concerns copolymers containing hexafluoropropylene and tetrafluoroethylene which are amorphous. They may be produced by a novel high pressure continuous process.
Amorphous fluorinated polymers, particularly perfluorinated polymers, are highly useful, particularly as coatings and encapsulants, because of their unusual surface properties, low refractive index, low dielectric constant., and the relative ease of coating or encapsulating objects with such polymers. However, the use of such polymers has been limited because of their high cost, which usually derives from the high cost of the monomers and/or the high cost of the polymerization process to make the polymers. Therefore, such polymers, and the processes for making them, which are lower in cost are constantly being sought.
U.S. Pat. No. 3,062,793 describes amorphous copolymers of tetrafluoroethylene (TFE) and hexafluoropropylene (HFP) which are made by a high pressure free radical polymerization. The only process described therein is a batch process which has a relatively low productivity.
This invention concerns a continuous polymerization process, comprising, contacting at a pressure of about 41 MPa to about 690 MPa, and a temperature above about 200xc2x0 C., preferably about 200xc2x0 C. to about 400xc2x0 C., tetrafluoroethylene, hexafluoropylene, and a radical initiator, to produce an amorphous polymer which contains at least 30 mole percent, of repeat units derived from said hexafluoro-propylene, at least 1 mole percent of repeat units derived from said tetrafluoro-ethylene, and provided that said continuous polymerization has an average residence time of about 5 seconds to about 30 minutes.
This invention also concerns an amorphous polymer, consisting essentially of repeat units of the formula:
(a) at least about 30 mole percent of
xe2x80x94CF2xe2x80x94CF(CF3)xe2x80x94xe2x80x83xe2x80x83(I)
(b) at least about 1 mole percent
xe2x80x94CF2xe2x80x94CF2xe2x80x94xe2x80x83xe2x80x83(II)
xe2x80x83and
(c) 0 to about 10 mole percent 
wherein X is xe2x80x94CnF2n+1 or xe2x80x94OCnF2n+1, m is 2, 3 or 4, and n is either an integer of 2 to 20 with alkyl groups xe2x80x94CnF2n+1 or an integer of 1-20 with alkoxy groups xe2x80x94OCnF2n+1.
provided that in said polymer less than 20 mole percent of (I) is present in the form of triads.
The invention also concerns a continuous polymerization process, comprising, contacting at a pressure of about 41 MPa to about 690 MPa, and a temperature of about 200xc2x0 C. to about 400xc2x0 C., tetrafluoroethylene, hexafluoro-propylene, and a third monomer and a radical initiator, to produce an amorphous polymer which contains at least 15 mole percent, preferably 30 mole percent of repeat units derived from said hexafluoropropylene, at least 0-70 mole percent of repeat units derived from said tetrafluoroethylene, and 0-70 mole percent of repeat units derived from said third monomer, and provided that said continuous polymerization has an average residence time of about 5 seconds to about 30 minutes.
This invention also concerns a compound of the formula (C4F9)2NSCF3.
A novel compound herein is R6R7CFSO2R8 wherein R6 is perfluoroalkyl, perfluoroalkyl containing one or more ether oxygen atoms, perfluoroalkoxy or perfluoroalkoxy containing one or more ether oxygen atoms, R7 is perfluoroalkyl or perfluoroalkyl containing one or more ether oxygen atoms, and R8 is perfluoroalkyl. It is preferred that each of R6, R7 and R8 independently contain 1 to 30 carbon atoms. It is also preferred that R8 is perfluoro-n-alkyl containing 1 to 20 carbon atoms. It is more preferred that R6 is perfluoro-n-propoxy, R7 is trifluoromethyl, and R8 is perfluoro-n-octyl. This compound is useful as an initiator for the polymerizations described herein.
Also disclosed herein is an amorphous polymer containing repeat units derived from:
27-60 mole percent hexafluoropropylene, up to 35 mole percent total of one or more second monomers, and the balance tetrafluoroethylene, provided that at least one mole percent of TFE is present in the polymer, and wherein said second monomer is ethylene, vinyl fluoride, trifluoroethylene, 3,3,3-trifluoro-propene, 2,3,3,3-tetrafluoropropene, 4-bromo-3,3,4,4-tetrafluoro-1-butene, CH2xe2x95x90CHO(Cxe2x95x90O)R2 wherein R2 is perfluoro-n-alkyl containing 1 to 8 carbon atoms, CH2xe2x95x90CHR3 wherein R3 is perfluoro-n-alkyl containing 1 to 8 carbon atoms, CH2xe2x95x90CH(Cxe2x95x90O)OR4 wherein R4 is CnFxHy wherein x+y=2n+1 and n is 1 to 8, chlorotrifluoroethylene, or allyltrimethoxysilane;
27-60 mole percent hexafluoropropylene, up to 5 mole percent total of one or more fourth monomers and the balance tetrafluoroethylene, provided that the polymer contains at least 1 mole percent tetrafluoroethylene, wherein said fourth monomer is perfluorocyclopentene, perfluorocyclobutene, CF2xe2x95x90CFCF2CN, CF2xe2x95x90CFR5 wherein R5 is perfluoroalkyl optionally containing one or more of one or more ether groups, one cyano group, or one sulfonyl fluoride group, perfluoro-(2-metylene-4-methyl-1,3-dioxolane), perfluoro(2-methyl-2,3-dihydro-1,4-dioxin), or FSO2CF2CF2OCF(CF3)CF2OCFxe2x95x90CF2; or
up to 30 mole percent total of one or more second monomers and up to 5 mole percent total of one or more fourth monomers.
Described herein is an amorphous copolymer, consisting essentially of:
(a)  greater than 15 mole percent of the repeat unit
xe2x80x94CF(CF3)xe2x80x94CF2xe2x80x94xe2x80x83xe2x80x83(I)
(b) at least 1 to about 60 mole percent of the repeat unit
xe2x80x94CF2xe2x80x94CF2xe2x80x94xe2x80x83xe2x80x83(II)
(c) about 0.1 to about 85 mole percent of the repeat unit
xe2x80x94CH2xe2x80x94CF2xe2x80x94xe2x80x83xe2x80x83(IV)
wherein no more than about 20 mole percent of (I) is present in triads.
Also described herein is an amorphous copolymer, consisting essentially of repeat units of the formula:
(a)  greater than 15 mole percent of the repeat unit
xe2x80x94CF(CF3)xe2x80x94CF2xe2x80x94xe2x80x83xe2x80x83(I)
(c) about 0.1 to about 85 mole percent of the repeat unit
xe2x80x94CH2xe2x80x94CF2xe2x80x94xe2x80x83xe2x80x83(IV)
wherein no more than about 20 mole percent of (I) is present in triads.
Described herein is an amorphous copolymer, consisting essentially of:
(a)  greater than 10 mole percent of the repeat unit
xe2x80x94CF(CF3)xe2x80x94CF2xe2x80x94xe2x80x83xe2x80x83(I)
(b) up to about 32 mole percent of the repeat unit
xe2x80x94CF2xe2x80x94CF2xe2x80x94xe2x80x83xe2x80x83(II)
(c) about 53 to about 85 mole percent of the repeat unit
xe2x80x94CH2xe2x80x94CF2xe2x80x94xe2x80x83xe2x80x83(IV)
wherein the sequence
xe2x80x94(CH2CF2)xe2x80x94(CH2CF2)xe2x80x94(CF2CH2)xe2x80x94xe2x80x83xe2x80x83(S1)
is present in an amount according to an equation
mole percent S1xe2x89xa70.23(mole percent VF2 in polymer)xe2x88x9210.2.
The TFE/HFP copolymer made herein is amorphous. By an amorphous polymer is meant that the polymer has a heat of melting of less than 1 J/g when measured by Differential Scanning Calorimetry (DSC) at a heating rate of 10xc2x0 C./min, in the case of a TFE/HFP dipolymer. This is measured on a xe2x80x9cfirst heatxe2x80x9d, that is virgin polymer is heated to at least 300xc2x0 C. in the DSC (at 10xc2x0 C./min), and the heat of melting, if any, is measured. In the case of terpolymers, where the residual third monomer is often removed from the polymer by heating for about four hours, at 150xc2x0 C., in a vacuum oven, DSC xe2x80x9csecond heatsxe2x80x9d, at 10xc2x0 C./min to at least 200xc2x0 C., were used.
These polymers are made via a continuous polymerization process in which the initial ingredients are fed to the reactor in an essentially continuous manner and in which the product stream is essentially continuously withdrawn at approximately the same rate at which the ingredients are added. Such types of reactions are generally known to the artisan, see for instance H. F. Mark, et al., Ed., Kirk-Othmer Encyclopedia of Chemical Technology, 3rd Ed., vol. 19, John Wiley and Sons, New York, 1982, p. 880-914. Such continuous reactors include continuous stirred tank reactors and pipeline (tubular) reactors. Under the conditions employed in the process as described herein, the productivity of the process is exceptionally high. By productivity herein is meant the weight of polymer produced in a unit volume of reactor in a unit volume of time. Productivities herein are reported as kg/L/hr.
The process described herein has typical productivities of about 0.8 to about 15 kg/L/hr. The Examples illustrate that typically higher polymerization temperatures give higher productivities. By contrast, a batch polymerization, making a somewhat similar polymer, reported in U.S. Pat. No. 3,062,793, has productivities (from the Examples) of about 0.01 to about 0.03 kg/L/hr, more than an order of magnitude less than that for the continuous process. This means a lower cost for polymer produced by the continuous process.
The process is run at a pressure of about 41 to about 690 MPa (xcx9c6,000 to xcx9c100,000 psi), preferably about 55 to about 172 MPa (xcx9c8,000 to xcx9c25,000 psi), more preferably about 62 to about 152 MPa (xcx9c9,000 to about 22,000 psi), and especially preferably about 69 to about 103 MPa (xcx9c10,000 to xcx9c15,000 psi). As pressure drops down towards 41 MPa the molecular weight of the polymers formed and the conversion of monomers to polymer both tend to drop.
It is preferred that solvents not be used in the process, since at these pressures the monomers, particularly HFP, usually dissolve the polymer. Nonetheless, solvents can be used in the reactor. If the final product is to be a polymer solution, making the polymer solution directly may be preferable, to reduce costs (see Example 43). Sometimes for convenience in handling, small quantities of initiator are best introduced when diluted to a larger volume with a small amount of solvent (see Example 51). Solvent may also be used for other reasons, such as to decrease the viscosity of the process mixture, or to help keep lines clear of polymer, particularly at lower pressures. When solvents are used it is preferred that they be essentially inert under process conditions. Useful solvents include perfluorodimethylcyclobutane and perfluoro(n-butyltetrahydrofuran).
The polymer is soluble in the monomer(s) under the process conditions. Therefore, one method of polymer isolation is to reduce the pressure below that required for solution of the polymer, and isolate the polymer from that, as by decantation, filtration or centrifugation. Indeed, it may not be necessary to reduce the pressure of the unreacted monomers to atmospheric pressure, but merely that required for phase separation of the polymer. Therefore these monomers can be recycled with only a xe2x80x9cpartialxe2x80x9d repressurization, thereby saving energy costs. Alternatively the pressure can be reduced to atmospheric pressure, while the volatile monomers are vented off, leaving the product polymer. The monomers can of course be recovered and reused.
The apparatus for running the polymerization may be any suitable pressure apparatus in which the reactant and products streams may be added and removed at appropriate rates. Thus the apparatus may be a stirred or unstirred autoclave, a pipeline type reactor, or other suitable apparatus. Agitation is not necessary, but preferable, especially to obtain polymers with low MWD""s. The material of construction should be suitable for the process ingredients, and metals such as stainless steel are often suitable.
The polymerization is carried out above about 200xc2x0 C., preferably from about 200 to about 400xc2x0 C., more preferably from about 225 to about 400xc2x0 C., and most preferably from about 250 to about 400xc2x0 C. The initiator is chosen so that it will generate active free radicals at the temperature at which the polymerization is carried out. Such free radical sources, particularly those suitable for hydrocarbon vinyl monomers at much lower temperatures, are known to the artisan, see for instance J. Brandrup, et al., Ed., Polymer Handbook, 3rd Ed., John Wiley and Sons, New York, 1989, p. II/1 to II/65. The preferred temperature for running our process depends on both the monomers and the initiator and is often a compromise between raising temperature to favor high productivities and high conversions and lowering temperature to minimize chain transfer and monomer degradation. For the copolymerization of HFP with TFE, for example, where chain transfer is not a problem, C2F5SO2C2F5 initiation is a good choice on account of the very high productivities it affords at 400xc2x0 C. For the polymerization of HFP/TFE/PMVE, however, where PMVE chain transfer is of prime concern, NF3 which retains good efficiency at 250xc2x0 C., is an excellent choice for initiator.
Suitable free radical initiators include NF3, RfNF2, Rf2NF, Rf3N, R1Nxe2x95x90NR1, RfOORf, perfluoropiperazine, and hindered perfluorocarbons of the formula CnF2n+2 such as are described in World Patent Application 88/08007, wherein each Rf is independently perfluoroalkyl, preferably containing 1 to 20 carbon atoms, hindered perfluoroalkenes of the formula CnF2n, perfluoro-(dialkylsulfones) of the formula R1SO2R1, perfluoroalkyl iodides of the formula R1I, R1SO2F, R1SO2Cl, ClSO2Cl, perfluoroalkylene diiodides of the formula IR6I where the two iodides are not vicinal or geminal wherein R6 is perfluoroalkylene containing 3 to 20 carbon atoms, perfluoro(dialkyldisulfides) R1SSR1, and perfluoroalkyl compounds containing nitrogen-sulfur bonds of the formula R12NSR1, wherein each R1 is independently saturated perfluorohydrocarbyl optionally containing one or more ether groups, isolated iodine, bromine or chlorine substituents, or perfluoroamino groups. By xe2x80x9csaturated perfluorohydrocarbylxe2x80x9d is meant a univalent radical containing only carbon and fluorine and no unsaturated carbon-carbon bonds. By an xe2x80x9cisolatedxe2x80x9d iodine, bromine or chlorine substituent is meant that there are no other iodine, chlorine of bromine atoms on carbon atoms alpha or beta to the carbon atom bonded to the isolated iodine, bromine or chlorine atom. All of these initiators are illustrated in one or more of the Examples. Some of these initiators may only be active at the higher end of the temperature range of the polymerization process. This too is illustrated in the Examples, and the activity of any particular initiator molecule may be readily determined by minimal experimentation. Preferred initiators are NF3 Rf2NF, RfNF2, perfluoropiperazine, perfluoro(dialkylsulfones), i.e. R1SO2R1, and hindered perfluorocarbons. NF3 is an especially preferred initiator. If higher molecular weight polymers are desired, the initiator should preferably not have any groups present in its structure that cause any substantial chain transfer or termination during the polymerization. Such groups usually include, for instance, organic bromides or iodides or carbon-hydrogen bonds.
The amount of free radical initiator used will vary depending on process conditions. Generally speaking an effective amount is used, an effective amount being that which causes more polymerization to take place with the initiator than without. It is likely that any polymerization without deliberately added initiator present is due to adventitious impurities which can act as initiators at the high polymerization temperatures. Effort should be made to minimize these impurities, such as oxygen. A useful range of initiator concentration has been found to be about 0.003 to about 0.5 g of initiator/kg monomer, preferably about 0.1 to about 0.3 g/kg. Higher or lower amounts are also useful depending upon the initiator, the monomers, goal molecular weights, process equipment, and process conditions used, and can readily be determined by experimentation. The initiator may be added to the reactor as a solution in the monomer(s).
While xe2x80x9csolventsxe2x80x9d may be added to the polymerization so that the polymerization is carried out in solution or slurry, it is preferred if little or no solvent is added. The polymer formed is often soluble in the supercritical HFP under the process conditions. The polymer may be isolated simply by reducing the pressure below about 34 MPa (xcx9c5,000 psi), at which point the polymer becomes insoluble. The polymer may also be isolated as fibers or fibrils by flash spinning from solvent and by direct flash spinning of the polymerization mixture. Small amounts of solvents may be used for convenience, as for a carrier for the initiator. FC-75, perfluoro(2-n-butyltetrahydrofuran), and the cyclic dimer of HFP are examples of useful solvents. Another useful solvent is supercritical CO2.
The polymer produced by the instant process is amorphous. Whether this type of a polymer would be amorphous depends on the composition (relative amounts of HFP and TFE and other monomers if present), and the distribution of the two repeat units in the polymer. If a dipolymer, the polymer product should preferably contain at least about 30 mole percent of (I) and at least 1 mole percent of (II), preferably at least 30 mole percent of (II), more preferably about 35 to about 50 mole percent of (I) and about 50 to about 65 mole percent of (II) when a dipolymer is made [no repeat unit (III) present]. Optionally up to about 10 mole percent of repeat unit (III) may be present. When (III) is present a preferred composition is about 35 to about 65 mole percent (I), about 35 to about 65 mole percent (II), and about 0.1 to about 10 mole percent of (III). Various comonomers (III) may be used in the polymerization process, and be incorporated into the polymer. Perfluoro(alkyl vinyl ethers) and perfluorinated terminal alkenes, each optionally substituted with ether, cyano, halo (other than fluorine), sulfonyl halide, hydrogen or ester groups may be used. Also unfluorinated or partially fluorinated olefins or vinyl ethers, optionally substituted as above, may also be used. Useful comonomers include CF2xe2x95x90CFOCF2CF(CF3)OCF2CF2SO2F, ethylene, propylene, isobutylene, vinylidene fluoride, vinyl fluoride, trifluoroethylene, 3,3,3-trifluoropropene, 2,3,3,3-tetrafluoropropene, 4-bromo-3,3,4,4-tetrafluoro-1-butene, perfluoro(8-cyano-5-methyl-3,6-dioxa-1-octene), CF2xe2x95x90CF(CF3)COF, CH2xe2x95x90CHO(C=O)R2 wherein R2 is perfluoro-n-alkyl containing 1 to 8 carbon atoms, CH2xe2x95x90CHR3 wherein R3 is perfluoro-n-alkyl containing 1 to 8 carbon atoms, CH2xe2x95x90CH(Cxe2x95x90O)R4 wherein R4 is CnFxHy wherein x+y=2n+1 and n is 1 to 8, allyltrimethoxysilane, perfluorocyclopentene, perfluorocyclobutene, CF2xe2x95x90CFCF2CN, CF2xe2x95x90CFR5 wherein R5 is perfluoroalkyl optionally containing one or more of one or more ether groups, cyano groups, and/or sulfonyl fluoride groups and preferably only one cyano or sulfonyl fluoride is present, perfluoro(2-methylene-4-methyl-1,3-dioxolane), perfluoro(2-methyl-2,3-dihydro-1,4-dioxin), FSO2CF2CF2OCF(CF3)CF2OCFxe2x95x90CF2, methyl vinyl ether, CFClxe2x95x90CF2, CH2xe2x95x90CFCF3, CH2xe2x95x90CHCF3, CH2xe2x95x90CHCF2CF2CF2CF3, CH2xe2x95x90CHCF2CF2Br, CF2xe2x95x90CFCF2CN, and CF2xe2x95x90CFCF2OCF2CF2SO2F. In preferred compounds R2 is trifluoromethyl, R3 is trifluoromethyl or perfluoro-n-butyl, R4 is 1,1,1,3,3,3-hexafluoroisopropyl, and R5 is xe2x80x94CF2CN.
The above monomers (and others) can be used to make copolymers containing repeat units derived from HFP, TFE and one or more of the above monomers of the following compositions, and in these compositions:
 greater than 30 mole percent HFP, up to 25 mole percent X with the balance TFE, provided the polymer contains at least 1 mole percent TFE, wherein X is ethylene propylene, isobutylene, or methyl vinyl ether;
 greater than 15 mole percent HFP, 0.1 to 85 mole percent vinylidene fluoride, and up to 60 mole percent TFE (note that this polymer may also be a dipolymer of HFP and vinylidene fluoride), preferably  greater than 20 mole percent HFP, 0.1 to 75 mole percent vinylidene fluoride and up to 60 mole percent TFE, and more preferably  greater than 30 mole percent HFP, 0.1 to 65 mole percent vinylidene fluoride and up to 60 mole percent TFE;
 greater than 30 mole percent HFP, up to 2 mole percent CF2xe2x95x90CF(CF3)COF, with the balance TFE, provided the polymer contains at least 1 mole percent TFE;
27-60 mole percent HFP, up to 35 mole percent X, and the balance TFE provided that at least one mole percent of TFE is present in the polymer, wherein X is vinyl fluoride, trifluoroethylene, 3,3,3-trifluoropropene, ethylene 2,3,3,3-tetrafluoropropene, 4-bromo-3,3,4,4-tetrafluoro-1-butene, CH2xe2x95x90CHO(Cxe2x95x90O)R2 wherein R2 is perfluoro-n-alkyl containing 1 to 8 carbon atoms, CH2xe2x95x90CHR3 wherein R3 is perfluoro-n-alkyl containing 1 to 8 carbon atoms, CH2xe2x95x90CH(Cxe2x95x90O)OR4 wherein R4 is CnFxHy wherein x+y=2n+1 and n is 1 to 8, chlorotrifluoroethylene, and allyltrimethoxysilane, and preferred polymers contain 30-50 mole percent HFP, up to 20 mole percent X and the balance TFE, and more preferred polymer contain 30-45 mole percent HFP, up to 10 mole percent X and the balance TFE.
27-60 mole percent HFP, up to 5 mole percent X and the balance TFE provided that the polymer contains at least 1 mole percent TFE, wherein X is perfluorocyclopentene, perfluorocyclobutene, CF2xe2x95x90CFCF2CN, CF2xe2x95x90CFR5 wherein R5 is perfluoroalkyl optionally containing one or more of one or more ether groups, one cyano group, or one sulfonyl fluoride group, perfluoro(2-metylene-4-methyl-1,3-dioxolane), perfluoro(2-methyl-2,3-dihydro-1,4-dioxin), or FSO2CF2CF2OCF(CF3)CF2OCFxe2x95x90CF2, and preferred polymers contain 30-50 mole percent HFP, up to 2 mole percent X and the balance TFE.
In all polymers which contain a monomer other than HFP, TFE and vinylidene fluoride, it is preferred that minimum level of additional monomer is 0.05, more preferably 0.1 mole percent. Also more than one monomer xe2x80x9cXxe2x80x9d may be present in any of the above polymers. When the xe2x80x9climitationxe2x80x9d on any particular monomer or monomers xe2x80x9cXxe2x80x9d is a given percentage, the polymer may contain up to that percentage (total) of that xe2x80x9ctypexe2x80x9d of monomer in the polymer. For example a copolymer may contain up to 35 mole percent combined of trifluoroethylene and 3,3,3-trifluoropropene, or another polymer may contain up to 5 mole percent CF2xe2x95x90CFCF2CN and up to 30 mole percent 3,3,3-trifluoropropene. The total amount of xe2x80x9cXxe2x80x9d which may be in the copolymer may not exceed the highest amount for any of the individual monomers, as given above.
Polymer containing HFP, vinylidene fluoride (VF2) and optionally TFE may be analyzed by 19F NMR to determine the microstructure of the polymer. In particular, the microstructure of monomer sequences of isolated repeat units derived from HFP and xe2x80x9csurroundedxe2x80x9d by monomer units derived from VF2 may be determined. These are:
Herein the above sequences will be referred to by their Sequence No. For determining these sequences, 19F NMR spectra were acquired on 5% solutions in hexafluorobenzene (HFB). Spectra were taken at 80 C on a Bruker AC 250 operating at 235.4 MHz for 19F. The acquisition conditions included a 90 degree pulse width of 5.0 xcexcsec, 20 second recycle delay, and 64 co-added scans. Spectra were referenced to HFB at xe2x88x92162.46 ppm.
Composition was determined from the 19F NMR spectrum in the following way. Because of the high concentration of HFP, it was assumed that all VF2 next to HFP was represented by the signal at xe2x88x9275 ppm. VF2 which was non-adjacent to HFP was taken from the signal at xe2x88x9282 ppm. The sum of these areas was converted to moles of VF2. The amount of HFP was determined from the sum of the areas at xe2x88x9275 ppm and xe2x88x9270 ppm, converted into moles of HFP. In samples containing TFE, the TFE was determined from the area of the signals between xe2x88x9295 and xe2x88x92125 ppm corrected for CF2s from HFP and corrected for the CF2s from VF2 represented in the signal of HFP CF3s adjacent to CH2s from VF2 adjacent to CH2s from VF2.
For at least one sample, the composition of VF2 determined in this manner was confirmed by adding an internal standard of trifluoromethyldichlorobenzene to a weighed amount of polymer and determining the amount of CF2 from the 1H spectrum. For the sample tested, the results agreed within 3% relative.
HFP centered sequences were used as a way to identify differences in polymerization. The 19F signal at xe2x88x92179 to xe2x88x92179.5 ppm was identified as the CF in an HFP centered VF2/HFP/NVF2 sequence in which the CH2""s are beta to the CF. The signal at xe2x88x92180.4 to xe2x88x92181.2 ppm was identified as a CF in a VF2/HFP/VF2 sequence in which there were one CH2 alpha and one CH2 beta to the CF in the HFP. The final signal at xe2x88x92181 to xe2x88x92181.8 ppm was identified as VF2/HFP/NVF2 in which one CH2 is alpha and one CH2 is gamma and one CF3 is delta to the CF.
Amorphous polymer containing HFP, VF2, and optionally TFE or other monomers, but preferably only TFE, may also be analyzed by 13C NMR. These analyses may yield additional information about these polymers. In particular, VF2 centered sequences may be determined, see for instance F. A. Bovey, et al., Macromolecules, vol. 10, p. 559 et seq. (1977), and R. E. Cais, et al., Analytica Chimica Acta, vol. 189, p. 101 et seq. (1986), both of which are hereby included by reference. In particular the sequence
xe2x80x94(CH2CF2)xe2x80x94(CH2CF2)xe2x80x94(CF2CH2)xe2x80x94xe2x80x83xe2x80x83(S1)
may be detected by its signal at 42.5 ppm (vs. hexafluorobenzene internal standard, see below for 13C NMR procedure). Any of the repeat units in the polymers, including VF2 units, may be bonded to the end of this sequence. It has been found (see Examples 133 to 136, and their 13C analyses) that polymers containing 53 or more mole percent of VF2, preferably about 58 or more mole percent VF2, and about 10 or more mole percent HFP, preferably about 15 or more mole percent HFP, and optionally containing TFE, made using the high pressure/high temperature polymerization processes described herein have a higher amount of this sequence than similar polymers made by xe2x80x9cconventionalxe2x80x9d methods.
The mole percent of VF2 in S1 in the polymer, based on the total amount of VF2 in the polymer (from the 13C analysis) is represented by the equation
mole percent S1xe2x89xa70.23(mole percent VF2 in polymer)xe2x88x9210.2
More preferably, the mole percent of S1 is
mole percent S1xe2x89xa70.23(mole percent VF2 in polymer)xe2x88x929.8
All of the polymers herein may be crosslinked by methods known in the art. Perfluorinated polymers may be crosslinked by exposure to ionizing radiation. Polymers containing hydrogen or functional groups such as nitrile or sulfonyl halide may be crosslinked by methods known in the art. When crosslinked these polymers are of course crosslinked elastomers if their Tg is below ambient temperature.
As mentioned above, the properties of the polymer will be affected not only by the overall composition of the polymer, but by the distribution of the various monomer units in the polymer. The instant process yields a polymer in which the monomer units are more uniformly distributed in the polymer, which gives polymer with more consistent properties. One measure of polymer uniformity is randomness of the monomer units in the polymer. A measure of this is relative amounts of isolated repeat units, diads, triads etc. By diads and triads are meant instances in which two or three repeat units from the same monomer, respectively, occur in the polymer.
Many of the polymers (including some of the polymers containing 3 or more different repeat units) made by the process described herein have relatively small amounts of triads of repeat unit (I), which of course derived from HFP. Thus in such polymers less than 20 mole percent of (I) is in the form of triads, and preferably less than about 15% and more preferably less than about 10%. As would be expected, in polymers with higher amounts of (I), there is a tendency towards higher triad content. The amount of triads in the polymer can be determined by 19F NMR (see below for procedure). See the summary of triad data for polymers prepared in Examples 23 and 33-36 in the table following Examples 45 to 49. See Examples 23 and 33-36 and Comparative Example 1 for triad amounts in various polymers.
The instant polymers also have a narrower molecular weight distribution (MWD) than prior art polymers. By MWD is meant the weight average molecular weight divided by the number average molecular weight (Mw/Mn). Polymers described herein often have MWD""s of less than 5, preferably less than 4. Such polymers often have a better combination of processability and physical properties.
Repeat unit (III) may be present to help suppress crystallization and/or lower a glass transition temperature, or for other purposes, and are derived from the corresponding xcex1-perfluoroolefin, perfluorocycloolefin or perfluoro(alkyl vinyl ether). Preferred monomers for unit (III) in which xe2x80x94CnF2n+1 is present are those in which CnF2n+1 is perfluoro-n-alkyl. When X is xe2x80x94CnF2n+1 it is preferred if n is 2 to 14, while if X is xe2x80x94OCnF2n+1 it is preferred if n is 1 to 4, more preferably 1 or 3.
Since TFE is considerably more reactive in the polymerization than HFP, an excess of HFP is needed to achieve the desired polymer composition. Typically this also means that at the end of the polymerization, much or all of the TFE will have polymerized, but there will be (a considerable amount of) unpolymerized HFP. In a sense this is an advantage, since the HFP can act to help carry the polymer from the reactor, and no additional carrier (such as a solvent) is needed. Typically the TFE will be about 1 to 15 mole percent of the total amount of monomer being fed to the process, with the HFP and other monomer(s) (if present) being the remainder.
The average residence time is the average amount of time any of the material fed to the reactor actually spends in the reactor, and is a function of the volume of the reactor and the volumetric flow of the process ingredients through the reactor. A preferred residence time is about 20 sec to about 10 min, more preferably about 30 sec to about 5 min, especially preferably about 40 sec to about 2 min. A minimum preferred residence time is about 10 sec., more preferably about 15 sec. A maximum preferred residence time is 10 min.
When the process fluids are being added to the reactor, it is preferred if they are preheated just before they enter the reaction to a temperature somewhat less than that of the actual reactor temperature, about 20xc2x0 C. to about 100xc2x0 C. less. This allows one to maintain a uniform constant temperature in the reactor itself, and for the newly added materials to start the polymerization reaction immediately upon entry to the reactor.
The amorphous polymers described herein are useful in a variety applications, many of which are related to the fact that the polymers are readily soluble in certain halogenated, especially perfluorinated solvents, and so the polymers are readily useable as films, coatings and encapsulants. Useful solvents include xe2x80x9cdimerxe2x80x9d, perfluorobenzene, perfluoro(n-butyltetrahydrofuran), and FC-10 (tradename of xe2x80x9cdimerxe2x80x9d 3M fluorocarbon fluid). Another type of useful solvent is a perfluorinated (organic) compound containing sulfur, such as perfluoro-1,4-dithiane, perfluorothiepane, perfluorodiethylsulfone, and perfluorooctanesulfonyl fluoride.
In one preferred form, the solvent used to form solutions of the amorphous polymers herein is a mixed solvent. By a mixed solvent is meant a solvent that contains two or more liquid compounds that are miscible with each other in the proportion used. The compounds in the mixed solvent need not be solvents for the amorphous polymer if used alone, but it is preferred that at least one of the compounds of the mixed solvent is a solvent for the amorphous polymer. It is preferred that one of the compounds of the mixed solvent be a perfluorinated compound, as described in the preceding paragraph. Another preferred compound is a hydrofluorocarbon or hydrochlorofluorocarbon as described in Example 128. A preferred procedure for forming a solution of the amorphous polymer in a mixed solvent is to dissolve the amorphous polymer in a perfluorinated compound, and then add the other compound(s).
Since the polymers are relatively chemically resistant, they may be used to encapsulate articles which must be protected from contamination, corrosion and/or unwanted adhesion to other materials. Films and coatings may be particularly useful because of the inherent properties of the polymer, such as, lack of crystallinity (polymer is clear), low surface energy (and hence poor wetting by water or most organic liquids), low dielectric constant, low index of refraction, low coefficient of friction, low adhesion to other materials, etc.
The TFE/HFP copolymers (including di- and terpolymers) of this invention can be used in many ways. One use is as a processing aid in polyolefins. This aspect of the invention is discussed in detail below.
The TFE/HFP and TFE/HFP/(III) copolymer solutions and copolymer/solvent systems of this invention can be used in many ways, making it possible to achieve end results that could not be achieved with previously available perfluoropolymers or could be achieved only in less convenient ways. These results include any of the results for which polymer solutions are used, such as coating, encapsulation, impregnation, and the casting of film. The copolymer solutions and copolymer/solvent systems of the invention can be employed in any of the methods by which solutions are known to be used, including dipping, painting, and spraying.
The copolymer solutions and copolymer/solvent systems of this invention can be used to make coatings on a broad range of substrate materials, including metal, semiconductor, glass, carbon or graphite, and natural and synthetic polymers. The substrates can be in a broad range of physical forms, including film or paper, foil, sheet, slab, coupon, wafer, wire, fiber, filament, cylinder, sphere, and other geometrical shapes, as well as in a virtually unlimited number of irregular shapes. Coatings can be applied by methods known in the art, including dipping, spraying, and painting. For plane substrates of suitable dimensions, spin coating can be employed. Porous substrates can also be coated or impregnated. These include, for example, screens, foams, microporous membranes, and woven and non-woven fabrics. In making such coatings, the solvent can be driven off by heat leaving a dry copolymer coating. Another advantage is that extremely thin coatings can be achieved, as thin as 100 angstroms or possibly even thinner depending on the coating characteristics required.
Coatings of the copolymers of this invention can be a sole coating on a substrate, or a component of a multilayer coating. For example, a TFE/HFP copolymer coating of this invention can be used as a first or primer, intermediate, or final coating in a multilayer fluoropolymer coating system. The coatings of this invention include coatings resulting from several successive applications of solution or copolymer/solvent systems to increase coating thickness to desired levels.
Coatings of this invention can consist of the copolymers of this invention alone, or of the copolymers admixed with minor amounts of other materials either soluble in the solvent or dispersed in the coating solution, suspension, or copolymer/solvent system. A minor amount can be up to about 10 wt % based on the combined weight of copolymer and additive.
Specific coated articles are within the scope of this invention.
Coated articles include polymer extrusion dies and molds for rubber and plastic parts, such as o-rings, bottle caps, golf balls, golf ball covers, golf ball cover half shells, and the like. The copolymers of this invention can be used in coatings. Both interior and exterior surfaces of extrusion dies may be coated to, respectively, facilitate extrusion and alleviate die drip buildup.
Coated articles include gasoline engine carburetor parts; internal parts of internal combustion engines such as valves and piston skirts; razor blades; metal containers such as cans, pans, trays, vessels, and the like; metal sheets and foils; continuous metal belts, metal rods, tubes, bars, profiles, and the like; bolts, nuts, screws, and other fasteners.
Coated articles include an article bearing a machine-readable marking on at least one surface, especially but not limited to a tag that can be attached to another object to provide information about inventory identification, contents, ownership, hazards, operating conditions, or maintenance requirements, for example.
Coated articles include wire for electrical and mechanical service. In either case, the metal wire may be solid or stranded. Wires for mechanical service include catheter guide wire and the actuating wire of push-pull cable.
Coated articles include rubber o-rings, seals, beading, gasketing, fish hooks, and the like.
Coated articles include paper and textile materials, including woven fabric including glass fabric, non-woven fabric, felts, and the like, fibers including filaments, yarns, e.g., staple and continuous filament, and strands.
Coated articles include foams, membranes, and the like.
Coated articles include optical fibers in which the substrate is a glass or plastic fiber.
Coated articles include semiconductors, semiconductor devices, magnetic storage media including disks, photoconductors, electronic assemblies, and the like, wherein the coating thickness may be as little as 200 angstroms or even as little as 100 angstroms or even as little as 50 angstroms. Use of solutions containing low concentrations of the TFE/HFP copolymer of this invention, e.g., as low as 0.001 wt % copolymer can be especially advantageous to form these very thin coatings.
One use for the TFE/HFP copolymers of this invention is as a processing aid in polyolefins. When the TFE/HFP copolymer of this invention is used as a processing aid in the polyolefin for film applications, the polyolefin generally will have a melt index (ASTM D-1238) of 5.0 or less at 190xc2x0 C., preferably 2.0 or less. For high-shear melt processing such as fiber extrusion or injection molding, even high-melt-index resins, for example, those having a melt index of 20 or more, may suffer processing difficulties. Such polyolefins may comprise any thermoplastic hydrocarbon polymer obtained by the homopolymerization or copolymerization of one or more monoolefins of the formula CH2xe2x95x90CHRxe2x80x2 wherein Rxe2x80x2 is an alkyl radical, usually of not more than eight carbon atoms. In particular, this invention is applicable to the following: polyethylene, both of the high-density type and the low-density type having densities within the range 0.89-0.97; polypropylene; polybutene-1; poly(3-methylbutene); poly(4-methylpentene); and linear low density copolymers of ethylene and an alpha-olefin, such as propylene, butene-1, pentene-1, hexene-1, heptene-1, octene-1, decene-1, octadecene-1, or n-methylpentene-1.
Because of the different melt characteristics of the olefin polymers mentioned, the addition of the fluoropolymer process aids of this invention may be of greater value in some polyolefins than in others. Thus, polyolefins such as polypropylene and branched polyethylene, that have low molecular weight or broad molecular weight distributions and, therefore, have good melt flow characteristics even at low temperature, may not require the use of the fluoropolymer additives or be noticeably improved by them, except under unusual, adverse extrusion conditions. However, for polymers such as high molecular weight, high density polyethylene or linear low density ethylene copolymers, particularly those with narrow or very narrow molecular weight distributions, addition of the fluoropolymers is especially beneficial.
Such polyolefins are typically processed by extrusion techniques at melt processing temperatures Tp in the range of 175-275xc2x0 C. The commercially important blown-film process is usually carried out at Tp in the range of 200-250xc2x0 C., and commonly at 200-230xc2x0 C.
The polyolefins and thus the polymer blend composition containing the fluoropolymer processing aid may contain assorted additives used in the art, such as but not limited to antioxidants, acid scavengers, light stabilizers, pigments, slip agents, and lubricants. In particular, finely divided solids such as silica or talc may be incorporated as antiblock agents.
The concentration of fluoropolymer processing aid in the host resin at fabrication into the final article should be high enough to achieve the desired effect in improving processibility, but not so high as to have adverse economic impact. The amount required can vary with the effect desired, the host resin, additives used in the host resin, and the processing conditions which may be different from the laboratory conditions reported in the following examples. Under certain conditions, concentrations of 100 ppm or less, as low as 50 ppm or even 25 ppm, can be effective. Under other conditions, the effective amount may be 1000, 2000, or even 5000 ppm. For special purposes, concentrations of 10% or even 25% may be appropriate. Thus from about 25 ppm to about 25% by weight of the fluoropolymer may be present, with preferred ranges being from about 100 ppm to about 10% by weight, and even more preferable, about 100 ppm to about 2000 ppm by weight of the fluoropolymer. The fluoropolymer processing aid can be incorporated into the host resin at the desired final concentration, or can be incorporated into a masterbatch or concentrate that is added to the host resin in a ratio calculated to yield the desired final concentration.
A novel compound herein is R6R7CFSO2R8 wherein R6 is perfluoroalkyl, perfluoroalkyl containing one or more ether oxygen atoms, perfluoroalkoxy or perfluoroalkoxy containing one or more ether oxygen atoms, R7 is perfluoroalkyl or perfluoroalkyl containing one or more ether oxygen atoms, and R8 is perfluoroalkyl. It is preferred that each of R6, R7 and R8 independently contain 1 to 30 carbon atoms. It is also preferred that R8 is perfluoro-n-alkyl containing 1 to 20 carbon atoms. It is more preferred that R6 is perfluoro-n-propoxy, R7 is trifluoromethyl, and R8 is perfluoro-n-octyl. This compound is useful as an initiator for the polymerizations described herein.
In the Examples, the 19F NMR, which is used to determine the HFP distribution in the polymer, was measured on Bruker AC 250 NMR operating at 235 MHz. Polymer samples were loaded in 5 mm NMR tubes and heated to 250 to 360xc2x0 C. in a narrow bore probe. In the melt, the methine CF""s of the HFP units appear at xe2x88x92183.5 ppm if present as isolated units, at xe2x88x92179.5 if present as head to tail diads, and at xe2x88x92177 ppm if present as head to tail triads. It is uncertain whether or not the integration for the HFP triads at xe2x88x92177 ppm also includes higher (than triads) oligomeric blocks. The amount of HFP triads was determined from the ratio of the areas of the 19F NMR signal at xe2x88x92177 ppm to the total areas of the signals at xe2x88x92177, xe2x88x92179.5 and xe2x88x92183.5 ppm.
In the Examples, 13C NMR spectra were obtained using 20 weight percent solutions of the polymers in hexafluorobenzene. Spectra were taken at 60xc2x0 C. on a Bruker AMX 360 spectrometer operating at 90.5 MHz, using proton but not fluorine decoupling, 90xc2x0 pulses, inverse gated decoupling, a 30 second recycle delay, and taking 500-2000 coadded scans per sample. Vinylidene fluoride centered sequences were identified using much the same methodology described in F. A. Bovey, et al., Macromolecules, vol. 10, p. 559 et seq. (1977), and R. E. Cais, et al., Analytica Chimica Acta, vol. 189, p. 101 et seq. (1986).
In the Examples, pressure change was used to calculate the weight of tetrafluoroethylene (TFE) added to the mixing reservoir (2). For the tetrafluoroethylene calculations in Examples 1-13, 50, 51 and 65, gauge pressure of TFE was incorrectly assumed to be absolute pressure. Based upon this incorrect assumption the quantity 160 g of TFE was shown for Examples 1-13, 50, 51 and 65. The actual TFE added in these Examples was about 217 g to 228 grams. The actual amounts of TFE that were added are shown and labeled as such in parenthesis in Examples 1 and 50,51 and 65. The table on page 12 showing Examples 1-13 reflects the actual TFE measured.
In the Examples, the following abbreviations are used:
8CNVExe2x80x94perfluoro(8-cyano-5-methyl-3,6-dioxa-1-octene)
Conv.xe2x80x94conversion
GPCxe2x80x94gel permeation chromatography
HFPxe2x80x94hexafluoropropylene
I.D.xe2x80x94inside diameter
IRxe2x80x94infrared (spectrum)
Mnxe2x80x94number average molecular weight
Mwxe2x80x94weight average molecular weight
Mvxe2x80x94viscosity average molecular weight
O.D.xe2x80x94outer diameter
PETxe2x80x94poly(ethylene terephthalate)
PMVExe2x80x94perfluoro(methyl vinyl ether)
TFExe2x80x94tetrafluoroethylene
TGAxe2x80x94thermogravimetric analysis
VF2 or VF2xe2x80x94vinylidene fluoride
In the Examples, the following materials are used:
xe2x80x9cdimerxe2x80x9dxe2x80x94a perfluorinated solvent which is defined in U.S. Pat. No. 5,237,049
FC-40xe2x80x94Fluorinert electronic liquid sold by 3M Industrial Chemicals Division, thought to be substantially perfluoro(tributylamine).
FC(copyright)xe2x80x9475xe2x80x94Fluorinert(copyright) Electronic Liquid, sold by 3M Industrial Chemicals Products Division, thought to be substantially perfluoro(2-butyl-tetrahydrofuran)
Kalrcz(copyright) Perfluoroelastomer Partsxe2x80x94a tetrafluoroethylene/perfluoro(methyl vinyl ether) and curesite monomer copolymer part available from E. I. du Pont de Nemours and Company, Inc., Wilmington, Del., USA
Kapton(copyright) Polyimide Filmxe2x80x94a polyimide film available from E. I. du Pont de Nemours and Company, Inc., Wilmington, Del., USA
Mylar(copyright) Polyester Filmxe2x80x94a poly(ethylene terephthalate) film available from E. I. du Pont de Nemours and Company, Inc., Wilmington, Del., USA
Nordel(copyright) Hydrocarbon Rubberxe2x80x94an EPDM elastomer available from E. I. du Pont de Nemours and Company, Inc., Wilmington, Del., USA
PETxe2x80x94poly(ethylene terephthalate)
Viton(copyright) Fluoroelastomerxe2x80x94a copolymer of vinylidene fluoride, hexafluoropropylene, and optionally tetrafluoroethylene made by free radical polymerization in aqueous emulsion, in a continuous process, and available from E. I. du Pont de Nemours and Company, Inc., Wilmington, Del., USA